1. Field of the Invention
Aspects of the present invention relate to a flat panel display using a signal transmission method for transmitting a differential signal, and more particularly, to a flat panel display including a differential signaling system for an impedance matching in the signal transmission method.
2. Description of the Related Art
The cathode ray tube (CRT) is a widely used type of display device. The CRT has been used as a monitor for a television, a measuring instrument, or an information terminal. Due to limits on weight and size, CRT display devices are becoming unsuitable for an era where miniaturization and low weight requirements are essential.
Accordingly, various flat panel displays, such as a liquid crystal display (LCD), a plasma display panel (PDP), a field emission display (FED), and an organic light emitting display (OLED), have been studied and developed as substitutes for the CRT. These displays have advantages in light of miniaturization, light-weight, and low electric power consumption requirements, as compared to the CRT.
The flat panel display includes various components and wirings for transmitting signals between the components. Recently, with the development of electronic circuit and manufacturing process technology, signals can be transmitted through the wirings at high speed. These high speed signal transmission requirements lead to a requirement for a higher drive speed of the components.
Accordingly, various methods for transmitting signals between the components through wirings have been suggested, including a signal transmission method such as low voltage differential signal (LVDS) method or a reduced swing differential signaling (RSDS) method for transmitting a differential signal.
A differential signaling system transmits a different mode signal having the same amplitude and a different polarity through a differential transmission line. Accordingly, there is a tendency to remove a concentrated magnetic field and to couple an electric field. A high speed signal can be stably transmitted without a signal reflection or a skew (phase delay) electro magnetic interference (EMI) due to the coupled electric field.
A conventional flat panel display will be described with reference to the accompanying drawings. FIG. 1 is a block diagram showing a construction of a conventional flat panel display. The conventional flat panel display includes a display panel 40, a gate driver 20, a data driver 30, and a controller 10. Pixels are arranged at the display panel 40 in the matrix. The gate driver 20 sequentially applies a scan signal to gate wirings of the display panel 40. The data driver 30 applies an image signal DATA1 to data wirings of the display panel 40. The controller 10 applies the image signal DATA1 from an external graphic controller (not shown) to the data driver 30, and applies a control signal CS1 to the gate driver 20 and the data driver 30 in order to control a drive timing.
In the conventional flat panel display, after all gate wirings of the display panel 40 are sequentially scanned and the image signal DATA1 is applied to pixels through the data wirings to display one frame of an image, a vertical synchronous signal VSYNC is applied to display a next frame of the image.
FIG. 2 is a block diagram showing the controller and the data driver shown in FIG. 1 in detail. FIG. 3 is a view showing a signal transmission method between the controller and the data driver. As shown in FIG. 2, the data driver 130 is composed of a plurality of data driving circuits 132. The plurality of data driving circuits 132 receive image signals DATA [+,−] from the controller 110 through first and second wirings W1 and W2, and receive a control signal CS11 from the controller 110 through a third wiring W3.
The data driver 130 includes a plurality of data driving circuits 132 therein. The data driving circuits 132 receive image signals DATA [+,−] from the controller 110, and output the signals to the data wirings according to the control signal CS11 from the controller 110. A plurality of data wirings (not shown) are electrically coupled to the data driving circuits 132, and apply the image signals DATA [+,−] applied to the data driving circuits 132 to the pixels.
The image signal from the controller is transmitted to the respective data driving circuits in the aforementioned differential signal transmission method. As shown in FIG. 3, in order to transmit one data group DATA [+,−], a differential transmission line arrangement, namely, first and second wirings W1 and W2, are provided between the controller 110 (a sending end Tx) and the data driving circuit 132 (a receiving end Rx). A termination resistor Rt is installed between differential transmission lines of the receiving end (data driving circuit 132) side. The termination resistor Rt electrically connects the first wiring W1 and the second wiring W2 to each other, which are connected to each data driving circuit 132.
The image signal DATA [+] applied through the first wiring W1 is transferred to the controller 110 through the termination resistor Rt and the second wiring W2. The termination resistor Rt prevents excessive current from flowing to the data driving circuit 132. A voltage across the termination resistor Rt is image signal DATA [+,−], and is applied to the data driving circuit 132.
A plurality of electric devices and wirings are provided in the flat panel display, and are electrically coupled to each other. Since the electric devices and wirings have an impedance component, the signal is attenuated during a signal transmission between the electric devices.
The controller 110 and the data driving circuits 132 have an impedance component. The first and second wirings W1 and W2 connecting the controller 110 and the data driving circuits 132 have an impedance component Z0. If the impedance value Z0 of the first wirings W1 and W2 is different from that of the data driving circuits 132, namely, when an impedance mismatching occurs, the image signals DATA[+,−] are not supplied to the data driving circuits 132 correctly. A part of the image signals is reflected and discharged.
A reflection coefficient ┌ is expressed by the following equation 1.
                    Γ        =                                            Z              diff                        -                          R              t                                                          Z              diff                        +                          R              t                                                          (        1        )            
where a differential impedance Zdiff is a value less than 2Z0 and is a sum of impedance values of the first and second wirings, and has a different value according to a manufacturing process variable and a construction of the flat panel display.
When the differential impedance Zdiff is identical with a value of the termination resistor, a reflection loss of a signal does not occur. However, the differential impedance Zdiff varies. Accordingly, in the conventional case, the impedance matching is not normally achieved in the differential transmission method.
When a reflection wave occurs due to an impedance mismatching, an interference with the image signals DATA [+,−] applied through the first wiring W1 occurs to cause unstable wave, signal distortion, and attenuation. The electro magnetic interference (EMI) reduces image quality of the flat panel display.